Dissecting the role of TGFβ in pancreatic ductal adenocarcinoma

Watt, Dale M. (2021) Dissecting the role of TGFβ in pancreatic ductal adenocarcinoma. PhD thesis, University of Glasgow.

Abstract

Pancreatic Cancer is a disease of unmet clinical need with near uniform lethality. Genome sequencing of patient tumour samples has highlighted the transforming growth factor beta (TGFβ) signalling pathway to be one of the most dysregulated in pancreatic ductal adenocarcinoma (PDAC). TGFβ is proposed to drive tumour suppression through blockade of cell proliferation, while also having the capacity to induce epithelial mesenchymal transition (EMT) aiding cell escape and drug resistance. Further, it has potent effects as an immune suppressor and as an activator of fibroblasts, particularly pertinent in PDAC due to the abundance of cancer-associated fibroblast (CAF) infiltrate and extracellular matrix (ECM) deposition. Therefore, using a dual recombinase (DR) mouse model of PDAC I interrogated the function of TGFβ across multiple cell types at both tumour initiating time points and in established tumours.

I have demonstrated that TGFβ is a potent tumour suppressor, with deletion of the essential receptor component Alk5 accelerating oncogenic KrasG12D-driven tumourigenesis in pre-neoplastic pancreatic lesions, with development of PDAC noted. This novel model develops only pancreatic tumours and replicates the stepwise acquisition of genetic permutations observed in the progression of human disease, through the tamoxifen-controlled deletion of Alk5 in adult pancreas tissue. Previous Alk5 deleted models developed squamous stomach and skin tumours complicating their use in studying PDAC.

Altered biology was detected between the Alk5 deletion driven tumours compared to Pdx1-Flippase; FSF-KrasG12D/+; Trp53frt/+ (KPF) mouse tumours, highlighted through RNA sequencing of bulk tumour. Deletion of ALK5, or other components of the TGFβ signalling pathway, alongside oncogenic KRAS, is present in a large subset of PDAC patients, with the Alk5 depleted model potentially re-capitulating these tumours, thereby providing a pre-clinical model to test therapeutics. For instance, Gene Set Enrichment Analysis (GSEA) highlighted elevated p53 pathway enrichment and decreased enrichment of EMT genes in the Alk5 deleted model. Deletion of Alk5 in the cancer epithelium of established tumours in the KPF mice reduced the metastatic burden, although did not affect survival, with deletion of Tgfb1 showing similar findings. Thesefindings may be indicative of the pro-tumourigenic role of TGFβ signalling in EMT.

Stromal targeted therapies have had mixed efficacy in PDAC, with pre-clinical findings failing to be translated into human trials. I show that depletion of Alk5 or Tgfb1 across all CAFs, or in restricted population of myofibroblasts (myCAF) in established tumours does not affect survival. Although, deletion of Tgfb1 in the restricted myCAF population, but not across all fibroblasts, does alter the CAF population, reducing the abundance of myCAFs specifically. These findings indicated a dependence on fibroblast-derived, TGFβ mediated paracrine stromal crosstalk for maintaining myCAF populations in PDAC.

Neutrophils have been shown to play a role in the metastatic cascade of PDAC, with depletion reducing metastatic burden. TGFβ has been proposed to polarize neutrophils to a tumour promoting phenotype. I therefore investigated the neutrophil specific deletion of Alk5, in the KPF mice, observing no change in survival, but with alterations in metastasis noted. Neutrophil maturity was decreased in Alk5 deleted neutrophils, although further experimentation is required to confirm and clarify the relevance of these findings.

Collectively, my data has elucidated the dual role of TGFβ signalling in initiating and established tumour stages, while highlighting a stromal programming role of fibroblast produced TGFβ1 and implicating TGFβ signalling as a modulator of neutrophil maturity.

• Item Type: Thesis (PhD)
• Qualification Level: Doctoral
• Additional Information: Supported by funding from Cancer Research UK.
• Colleges/Schools: College of Medical Veterinary and Life Sciences > School of Cancer Sciences
• Supervisor's Name: Morton, Professor Jennifer P.
• Date of Award: 2021
• Depositing User: Theses Team
• Unique ID: glathesis:2021-82662
• Copyright: Copyright of this thesis is held by the author.
• Date Deposited: 02 Feb 2022 14:44
• Last Modified: 08 Apr 2022 16:54
• Thesis DOI: 10.5525/gla.thesis.82662
• URI: https://theses.gla.ac.uk/id/eprint/82662